Generally, the chassis of a vehicle such as an automobile is at ground potential. For this reason, there are many cases where a load such as a lamp or motor is placed on the low-potential side. Accordingly, heavy use is made of a high-side switch in which the load is connected between the switch and ground. Owing to low ON resistance and low cost, an N-channel MOSFET that performs a source follower operation frequently is used as the switch element.
If an overcurrent flows into the load in the case of such a high-side switch, there is the danger that damage may be inflicted upon the N-channel MOSFET or wiring material serving as the switch element. Accordingly, the general practice is to provide an overcurrent detecting circuit for detecting overcurrent and controlling the current that flows into the N-channel MOSFET. Patent Documents 1, 2 and 3 disclose techniques that use a wire constituting a semiconductor device as an element for detecting current that flows through an N-channel MOSFET in such an overcurrent detecting circuit.
As related art, Patent Document 4 describes a temperature detecting circuit for detecting temperature from a voltage difference utilizing the fact that the temperature coefficient of a voltage difference, which is produced across two diodes, differs depending upon the input current.
[Patent Document 1]
Japanese Patent Kokai Publication No. JP-A-11-121683
[Patent Document 2]
Japanese Patent Kokai Publication No. JP-P2004-80087A
[Patent Document 3]
Japanese Patent Kokai Publication No. JP-A-6-216307
[Patent Document 4]
Japanese Patent Kokai Publication No. JP-P2000-213992A